The invention relates to a method for the contactless detection of the position of a butterfly valve shaft of a butterfly valve connecting piece, the butterfly valve connecting piece having a housing which can be closed off by a lid, and a throttle orifice which is arranged in the housing, for a butterfly valve which is arranged on the butterfly valve shaft, the butterfly valve shaft being capable of being driven by an electric actuator drive and having, at one of its ends, a magnet which is arranged in contactless alignment with a sensor which is arranged on the lid. It also relates to a butterfly valve connecting piece having a housing which can be closed off by a lid, and having a throttle orifice which is arranged in the housing, for a butterfly valve which is arranged on a butterfly valve shaft, the butterfly valve shaft being capable of being driven by an electric actuator drive and having, at one of its ends, a magnet which is arranged in contactless alignment with a sensor which is arranged on the lid.
Butterfly valve connection pieces are generally used to control the quantity of fresh gas in a motor vehicle. Butterfly valve connecting pieces comprise a housing with a throttle orifice and a throttle element which is arranged in the throttle orifice. The throttle element generally comprises a butterfly valve which is arranged on a butterfly valve shaft and which is arranged so as to be capable of pivoting in the housing of the butterfly valve connecting piece. The butterfly valve assumes a specific position in the throttle orifice to permit a specific quantity of fresh gas to pass through. For this purpose, the butterfly valve shaft can be actuated mechanically or electromechanically.
When the butterfly valve shaft is actuated electromechanically, the butterfly valve connecting piece normally has a position detection device which can be used to detect the current position of the butterfly valve shaft. Depending on the respective current position of the butterfly valve shaft, a signal, with which the butterfly valve shaft can be actuated using the actuator drive arranged in the butterfly valve connecting piece, is then generated either inside or outside the butterfly valve connecting piece.
With respect to these position detection devices, a distinction is made between those in which contact with the butterfly valve shaft is at least indirectly necessary in order to detect the respective current position of the butterfly valve shaft, and on the other hand contactless position detection devices. A position detection sensor which is not contactless is a potentiometer in which a sliding contact which is coupled to the rotary movement of the butterfly valve shaft moves back a certain distance along a contact surface when there is a rotary movement of the butterfly valve shaft, the distance by which the sliding contact moves back being a measure of the rotary movement of the butterfly valve shaft. Such potentiometers are subject to a certain degree of wear which is decisively determined by the mechanical abrasion between the sliding contact and the contact path.
In order to reliably avoid mechanical wear of position detection devices which are not contactless, butterfly valve connecting pieces have been developed in which the detection of the rotary movement of the butterfly valve shaft can be carried out in a contactless fashion. An example of such a contactless sensor is a Hall sensor which is positioned in alignment with a ring magnet which is arranged on the butterfly valve shaft. This Hall sensor supplies a signal which is proportional to the magnetic induction B which is generated by the magnetic field of the ring magnet. The ring magnet generally comprises an outer shielding ring, and, in the interior, two flux permeable parts which are arranged approximately in parallel. The Hall sensor is then located in the gap between the two flux permeable parts. This principle is well protected against magnetic interference fields as they are kept away from the Hall sensor by the outer shielding ring. The linear, usable measuring range is however restricted to approximately two times 75° in the case of this principle. For this reason, the magnetic zero point cannot be positioned in the mechanical idling stop (butterfly valve closes the throttle orifice virtually completely) in order to detect the typical butterfly valve working range, and would therefore be outside the idling position of the butterfly valve. However, as the measuring precision is highest at the magnetic zero point and decreases with increasing distance from the magnetic zero point, the measuring precision in the idling range of the butterfly valve would then be smaller than in a range which is positioned between the idling range and the full load range. This does not correspond to the customary precision requirements made of a contactless position detection device for a butterfly valve shaft of a butterfly valve connecting piece in which the measuring precision is to be highest during idling.
Alternatively, the Hall sensor can project vertically into a parallel field which is formed between two magnet squares connected by means of a yoke, the magnet squares being permanently connected to the butterfly valve shaft. This principle is known from JP 8 068 606 A. The necessary signal amplification is carried out here in evaluation electronics which are connected to the Hall sensor via a punched grill. The electrical interface with the outside is also produced here by means of a punched grill or else lead frame which is formed into plug contacts at its ends. According to this principle, linearization is dispensed with in an angular range of approximately +/− 45° around the zero crossover, which involves concessions in terms of linearity. Given customary working angles of less than 90°, it is theoretically possible to detect the butterfly valve position if the zero crossover is positioned in the center of the measurement range. However, the idling range would then be located in a measurement range in which the linearity error rises excessively because the precision of a Hall sensor is actually highest around the zero crossover of the induction. The maximum errors would occur in the case of maximum actuation in the region of +/− 45°, that is to say full load and idling, as temperature drift and aging effects would then be felt. On the other hand, the measurement precision would be highest in the intermediate range. However, a position detection device which is provided for a butterfly valve connecting piece should be particularly high precisely with small angles of aperture of the butterfly valve, and thus particularly small rotary movements of the butterfly valve shaft. For this reason, this application is not particularly well suited for a position detection device of a butterfly valve shaft. In addition, the precision levels which are usually required cannot normally be achieved with this last-mentioned principle, even with particularly long operating times. It also proves disadvantageous that the open sides of the approximately U-shaped yoke are open to magnetic interference fields, and there is thus the risk of the sensor signal being falsified from the outside.
As an alternative to a Hall sensor it is possible to use a magnetoresistive sensor, referred to below as MR sensor, in a contactless position detection device for detecting a rotary movement of a butterfly valve shaft. The MR sensor requires a field which turns in the plane which is formed by the sensor structure. For this it is necessary for the sensor element to be arranged perpendicularly with respect to the shaft, and thus not in a plane parallel to the axis of rotation of the shaft. As the output characteristic curve of MR sensors is periodic at 180°, the linear usable angular range is restricted to approximately 45°. For this reason, an MR sensor also does not usually have the angular range of approximately 90° which is necessary to detect a rotary movement of the butterfly valve shaft.